Geological processes on the Northeast Atlantic Margin. Preliminary results of geological and geophysical investigations during the TTR-8 cruise of R/V Professor Logachev June-August 1998
Kenyon, N.H.; Ivanov, M.K.; Akhmetzhanov, A.M. (Ed.) (1999). Geological processes on the Northeast Atlantic Margin. Preliminary results of geological and geophysical investigations during the TTR-8 cruise of R/V Professor Logachev June-August 1998. Technical Series. Intergovernmental Oceanographic Commission = Série technique, 54. UNESCO: Paris. 141 + annex pp.
Part of: IOC Technical Series. Intergovernmental Oceanographic Commission = Série technique. UNESCO: Paris. ISSN 0074-1175
Geological processes at different locations along the European continental margin in the North Atlantic were studied on the TTR-8 cruise (1998) with a wide range of equipment. They included: single-channel seismic reflection profiling carried out simultaneously with OKEAN 10 kHz long-range side-scan survey, high-resolution survey with the OREtech deep-towed instrument comprising 30 and 100 kHz side-scan sonar and 5 kHz subbottom profiler units. For more detailed studies, a bottom TV survey and different techniques of bottom sampling were employed.The cruise data comprise more than 3000 km of seismic and long range side-scan sonar lines, 185 km of high resolution side-scan survey, about 20 km of bottom TV survey and 70 bottom samples.On the Portuguese margin west of Lisbon, the broad network of canyons was successfully mapped with the OKEAN side-scan sonar. The data add to and fit well with the seismic and side-scan sonar datasets collected previously in the area by Portuguese scientists.A study conducted in the Porcupine Seabight mud mound areas was aimed at obtaining further bottom samples for geochemical and microbiological investigations. A more detailed survey was carried out with 100 kHz side-scan sonar on one of the mounds. A better understanding of the seabed processes observed during the TTR-7 cruise (1997) was achieved as a result of this second visit.A slump affecting the upper part of the sedimentary section was mapped on the eastern Faeroes margin. Another large slide on the northern Faeroes margin was also visited and detailed studies showed the presence of a number of stages of slide development. The recognition of the latter can be crucial for the determination of potentially hazardous areas on the continental margins. The presence of a megaturbidite, whose formation is probably related to the giant Northern Faeroes slide, was observed in cores taken downslope from the slide.Investigations of the southeastern part of the Vøring Plateau adjacent to the Storegga Slide shed more light in this area known for its numerous fluid escape structures and possible gas hydrates presence. A bottom simulating reflector (BSR) was observed and in several places it was found to be pierces by diapiric structures disturbing the sedimentary cover and reaching the seafloor at some locations. Some of the pockmarks, well seen on the long range side-scan sonar data, were carefully studied with high-resolution acoustic tools and bottom TV. The latter revealed the presence of bottom biota activity possibly related to gas seepages, and direct observation of escaping fluids were made and videotaped. Many samples taken from the pockmarks contain gas-saturated sediments and concretions of carbonate minerals whose formation is very likely due to the methane oxidation.The complex morphology of the seabed mounds located in the northwestern part of the Vøring plateau was observed on the OREtech sonograph.The unique nature of the Haakon Mosby mud volcano located to the southwest of the Bear Isle was confirmed by extensive seismic and OKEAN survey. No other mud volcanoes were found although several mud diapiric structures were recognized and sampled.
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